erl_prim_loader

MODULE

erl_prim_loader

MODULE SUMMARY

Low Level Erlang Loader

DESCRIPTION

erl_prim_loader is used to load all Erlang modules into
the system. The start script is also fetched with this low level
loader.

erl_prim_loader knows about the environment and how to
fetch modules. The loader could, for example, fetch files using
the file system (with absolute file names as input), or a
database (where the binary format of a module is stored).

The -loader Loader command line flag can be used to
choose the method used by the erl_prim_loader. Two
Loader methods are supported by the Erlang runtime system:
efile and inet. If another loader is required, then
it has to be implemented by the user. The Loader provided
by the user must fulfill the protocol defined below, and it is
started with the erl_prim_loader by evaluating
open_port({spawn,Loader},[binary]).

Warning

The support for loading of code from archive files is
experimental. The sole purpose of releasing it before it is ready
is to obtain early feedback. The file format, semantics,
interfaces etc. may be changed in a future release. The functions
list_dir/1 and read_file_info/1 as well as the flag
-loader_debug are also experimental

EXPORTS

Starts the Erlang low level loader. This function is called
by the init process (and module). The init
process reads the command line flags -id Id,
-loader Loader, and -hosts Hosts. These are
the arguments supplied to the start/3 function.

If -loader is not given, the default loader is
efile which tells the system to read from the file
system.

If -loader is inet, the -id Id,
-hosts Hosts, and -setcookie Cookie flags must
also be supplied. Hosts identifies hosts which this
node can contact in order to load modules. One Erlang
runtime system with a erl_boot_server process must be
started on each of hosts given in Hosts in order to
answer the requests. See erl_boot_server(3).

If -loader is something else, the given port program
is started. The port program is supposed to follow
the protocol specified below.

This function fetches a file using the low level loader.
Filename is either an absolute file name or just the name
of the file, for example "lists.beam". If an internal
path is set to the loader, this path is used to find the file.
If a user supplied loader is used, the path can be stripped
off if it is obsolete, and the loader does not use a path.
FullName is the complete name of the fetched file.
Bin is the contents of the file as a binary.

The Filename can also be a file in an archive. For example
/otp/root/lib/mnesia-4.4.7.ez/mnesia-4.4.7/ebin/mnesia_backup.beam
See code(3) about archive files.

Retrieves information about a file. Returns
{ok, FileInfo} if successful, otherwise
error. FileInfo is a record
file_info, defined in the Kernel include file
file.hrl. Include the following directive in the module
from which the function is called:

The following protocol must be followed if a user provided
loader port program is used. The Loader port program is
started with the command
open_port({spawn,Loader},[binary]). The protocol is as
follows:

The erl_prim_loader module interprets the following
command line flags:

-loader Loader

Specifies the name of the loader used by
erl_prim_loader. Loader can be efile
(use the local file system), or inet (load using
the boot_server on another Erlang node). If
Loader is user defined, the defined Loader port
program is started.

If the -loader flag is omitted, it defaults to
efile.

-loader_debug

Makes the efile loader write some debug information,
such as the reason for failures, while it handles files.

-hosts Hosts

Specifies which other Erlang nodes the inet loader
can use. This flag is mandatory if the -loader inet
flag is present. On each host, there must be on Erlang node
with the erl_boot_server which handles the load
requests. Hosts is a list of IP addresses (hostnames
are not acceptable).

-id Id

Specifies the identity of the Erlang runtime system. If
the system runs as a distributed node, Id must be
identical to the name supplied with the -sname or
-name distribution flags.

-setcookie Cookie

Specifies the cookie of the Erlang runtime system. This flag
is mandatory if the -loader inet flag is present.